Global ice volume

Fig. 18-21 The last 250 000 years of environmental history, recorded in the central Antarctic ice sheet. Bottom three panels are data from the Vostok ice core (Lorius et al., 1990 Jouzel et at., 1993). Top panel is marine data representing global ice volume (Shackle-ton el al., 1990).

Fig. 18-22 The last 50 000 years of environmental history, recorded in central Greenland (GISP2 and GRIP ice cores), plus the CO2 record from Vostok, Antarctica, and global ice volume measured as sea level depression. (From top to bottom, references are Shackleton, 1987 Cuffey et ai, 1995 and Grootes et al, 1993 Cuffey and Clow, 1997 Chapellaz et al, 1990 Brook et al., 1996 Mayewski et al., 1997 Saltzman et al., 1997.)...

Fig. 4.3. (A) Composite multispecies benthic foraminiferal Mg/Ca records from three deep-sea sites DSDP Site 573, ODP Site 926, and ODP Site 689. (B) Species-adjusted Mg/Ca data. Error bars represent standard deviations of the means where more than one species was present in a sample. The smoothed curve through the data represents a 15% weighted average. (C) Mg temperature record obtained by applying a Mg calibration to the record in (B). Broken line indicates temperatures calculated from the record assuming an ice-free world. Blue areas indicate periods of substantial ice-sheet growth determined from the S 0 record in conjunction with the Mg temperature. (D) Cenozoic composite benthic foraminiferal S 0 record based on Atlantic cores and normalized to Cibicidoides spp. Vertical dashed line indicates probable existence of ice sheets as estimated by (2). 3w, seawater S 0. (E) Estimated variation in 8 0 composition of seawater, a measure of global ice volume, calculated by substituting Mg temperatures and benthic 8 0 data into the 8 0 paleotemperature equation (Lear et al., 2000).

Lear, C.H., Elderfield, H. and Wilson, P.A. (2000) Cenozoic deep-sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite. Science, 287, 269-272. 

Milankovitch cycles Changes in global ice volume that reach maxima every 23,000, 41,000, and 100,000 years. They are thought to be related to changes in astronomical alignments that have similar periods. 

Variations in the benthic foraminifera record after 33 Ma indicate fluctuations in global ice volume in addition to temperature changes. Since then the majority of the 5 0 variations can be attributed to fluctuations in the global ice volume. Thus, Tiedemann et al. (1994) demonstrated the presence of at least 45 glacial-interglacial cycles over the last 2.5 Ma. 

In spite of their limitations, the °Th and Pa methods have made an important contribution to the establishment of the Late Pleistocene chronology of deep-sea sediments. They provided the timescale upon which the deep-sea 5 0 record of global ice volume could be correlated with solar insolation, thus providing strong support for the astronomical theory of climate change (Broecker and Van Donk, 1970). 

Figure 12 Alkenone data acquired with planktonic foraminiferal can be used to remove the temperature effect from oxygen isotopic signals in order to assess global (ice volume) and regional (evaporation/precipitation balance) contributions to isotopic change. Data come from an equatorial Atlantic core studied by Schneider et al. (1996) the isotopic deconvolution was made by the present author. Note that the structure and amplitude of the temperature-corrected planktonic record are consistent with current thinking on the global ice volume signal for the late...

Much of what is currently understood about the Cenozoic history, of deep-sea temperature, carbon chemistry, and global ice volume, has been gleaned from the stable isotope ratios of benthic foraminifera. Benthic foraminifera extract carbonate and other ions from seawater to construct their tests. In many species, this is achieved near carbon and oxygen isotopic equilibrium. Kinetic fractionation effects tend to be small and constant (Grossman, 1984, 1987). As a result, shell fi C and strongly covary with the isotopic... 

Poore, R. Z. Matthews, R. K. 1984. Oxygen isotope ranking of Late Eocene and Oligocene planktonic foraminifers implications for Oligocene sea-surface temperatures and global ice volume. Marine Micropaleontology, 9, 111 -134. 

Figure 21.5 Estimate of surface temp>erature for the last 800,000 years, inferred from measurements of the ratio of O to 0 in fossil plankton that settled to the sea floor. The use of oxygen isotope ratios is based on the assumption that changes in global temperature approximately track changes in the global ice volume. Detailed studies for the last glacial maximum provide the temperature scale. Shown are changes in temperature (in C) from the modern value. Based on data from Imbrie et al. (1984) and presented by Crowley (1996).

Figure 20.7 Variation of global ice volume during the last 1 million years, inferred from the isotope record of deep-sea cores (After ref. [6])...

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